|Publication number||US7480056 B2|
|Application number||US 10/862,123|
|Publication date||Jan 20, 2009|
|Filing date||Jun 4, 2004|
|Priority date||Jun 4, 2004|
|Also published as||CA2509186A1, CA2509186C, US20050271395|
|Publication number||10862123, 862123, US 7480056 B2, US 7480056B2, US-B2-7480056, US7480056 B2, US7480056B2|
|Inventors||Ole Henrik Waagaard, Erlend Ronnekleiv|
|Original Assignee||Optoplan As|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (99), Non-Patent Citations (5), Referenced by (4), Classifications (10), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The present invention generally relates to time division multiplexed interferometric sensors. More specifically, the present invention relates to interrogating interferometric sensors in a manner that increases the allowable interrogation pulse duty-cycle and that improves signal-to-noise ratios.
2. Description of the Related Art
Time division multiplexing (TDM) of interferometric sensors is performed using pulsed light sources to produce pulse reflections from the sensors such that the reflections are distributed in time because of the different time delays associated with each sensor. The requirement that the reflections from the different sensors be separated in the time domain results in the need to use pulse duty cycles and pulse repetition rates that take into account the number of sensors being sensed and their separations.
An interferometric sensor may be described as being comprised of two paths from an interrogating transmitter unit to a receiver unit through an optical sensor network. The optical sensor network may comprise a number of paths, where certain pairs of paths form sensor interferometers. The different paths through the sensor network may typically be formed by optical waveguides and splitters like optical fibers, optical splitters, circulators, and other waveguide coupled components, or free space optical paths, mirrors, beam splitters and other bulk components. The time delay difference between the two paths of a sensor is called the imbalance of that sensor. The sensor imbalance can be made sensitive to some measurand that one wants to measure. Changes in the sensor imbalance are measured by extracting the phase of the interference between light components that has propagated the two paths as they are combined in the receiver. The extracted phase will thus provide information about the desired measurand. The portions of the sensor network that are common to both the sensor path and the reference path of a sensor may be called transport or lead paths. In a fiber optic sensor network the lead paths are called lead fibers.
Interferometric sensors can be multiplexed along the same fiber using time-division multiplexing (TDM). In TDM, the optical source outputs light with a periodic intensity pattern and with a repetition period T called the TDM repetition period. The duty-cycle of the source is defined as the fraction of time in which the source is turned on. The duty-cycle depends on the number of multiplexed sensors and the separation between the sensors. Each sensor directs a portion of the source light to the receiver. The sensors form different delays from the source to the detector, and signals directed from different sensors will therefore be separated in time at the detector.
A well-known time division multiplexed interrogation technique is the two pulse heterodyne sub-carrier generation technique as disclosed in J. P. Dakin, “An Optical Sensing System,” UK patent application number 2126820A (filed Jul. 17, 1982). The two pulse heterodyne technique repeatedly transmits two interrogation pulses that have pulse widths that are shorter than (or equal to) the sensor imbalance. The phase difference between the first and the second pulse of each pulse pair is linearly varied with time to produce a differential frequency shift between the sequences of first pulses and second pulses. In the two pulse heterodyne technique the second pulse that has propagated the shortest path of the interferometer and the first pulse that has propagated the longest path of the interferometer interfere, forming an interference pulse at the receiver which is detected and used for extraction of the sensor phase. The differential frequency shift between the first and second pulses of the pulse pairs produces a carrier frequency on the sequence of detected interference pulses. The phase of this carrier is extracted. This extracted carrier phase equals the sensor phase except for a constant phase term.
A well-known interrogation method for continuous wave (cw) interrogation of interferometric sensors is the phase generated carrier technique, disclosed in A. Dandrige et al., “Homodyne demodulation scheme for fiber optic sensors using phase generated carrier,” IEEE Journal of Quantum Electronics, 18(10):1647-1653, 1982. The phase generated carrier technique is based on a harmonic bias modulation of the sensor phase, for instance by modulation of the source phase, resulting in a detected interference signal that has signal components at harmonics of the source modulation frequency. The sensor phase (without the applied bias modulation) can be determined from a combination of the signal components of several harmonics of the source modulation frequency. This technique can also be used in combination with time-division multiplexing, see A. D. Kersey et al. “Time-division multiplexing of interferometric fiber sensor using passive phase-generated carrier interrogation,” Optics Letters, 12(10):775-777, 1987. The light source may then be pulsed in the same manner as for the two pulse heterodyne sub-carrier generation technique, while the source phase is modulated in the same manner as for the cw phase generated carrier technique. The detector is sampled at the arrival of the reflected pulses, and the sensor phase is calculated from the harmonics of the source modulation frequency.
One type of interferometric sensor is the inline Fabry-Perot sensor. When inline Fabry-Perot sensors are pulse interrogated, extra reflected pulses are received due to multiple reflections within the Fabry-Perot cavity. These pulses are called decay pulses. For Fabry-Perot interferometers, the number of decay pulses is in principle infinite. If for instance a decay pulse from sensor 1 arrives at the detector simultaneously with a detected interference pulse from sensor 2 that is used to calculate the sensor phase, the interference between the decay pulse and the detected interference pulse will introduce crosstalk from sensor 1 to sensor 2. Thus, the source duty-cycle and the delay separation between the sensors must be chosen so that the sequence of decay pulses has faded-out to a level that depends on the allowable crosstalk level. In the prior art, to suppress crosstalk between the inline Fabry-Perot sensors one set of decay pulses has to fade out before reflections from another pair of interrogation pulses can be received. Thus, most of the interrogation pulse duty-cycle is wasted by having to wait for the multiple reflections to fade. Other types of interferometric sensors have similar problems in that overlapping pulse reflections have to be prevented.
In view of the foregoing problems, an interferometric sensor interrogation method that increases the allowable interrogation pulse duty-cycle and that improves the signal-to-noise ratio would be beneficial.
Embodiments of the present invention generally provide for methods of interrogating time-multiplexed interferometric sensors using multiple interrogation pulses in a manner that increases the allowable interrogation pulse duty-cycle and that improves the signal-to-noise ratio.
According to embodiments of the present invention, in each TDM repetition period T, a sequence of Np>2 multiple interrogation pulses are generated in Np transmission time slots, where subsequent transmission time slots are separated by a sensor imbalance τs. Here the term “time-slot” refers to a period of time that occurs at the same position within every TDM repetition period. A phase modulator modulates the phase of the pulses such that the optical frequencies produced in different transmission time-slots are different. In a preferred embodiment, the difference in optical frequency between any two subsequent transmitted time-slots equals Δν, where Δν is the sub-carrier frequency. The portion of the m'th (m=0,1, . . . ,Np−1) interrogation pulse propagating the longest path of a sensor interferometer and the portion of the (m+1)'th interrogation pulse propagating the shortest path of the same interferometer will interfere, forming interference pulse number m out of a sequence of Np−1 interference pulses that arrives at the receiver within each TDM repetition period. The interference pulse number m arrives in receiver time slot number m within every TDM repetition period. The sequence of detected interference pulses from receiver time slot m in sequence of TDM periods will contain a sub-carrier signal component with frequency Δν. This sub-carrier signal will have a phase that is equal to the phase of the sensor apart from a constant bias phase. The sensor phase is calculated by combining phase information from sub-carrier signals extracted from several or all of the receiver time slots.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures.
The present invention provides for interrogating time-multiplexed interferometric sensors using multiple interrogation pulses in a manner that avoids the necessity of allowing all multiple reflections from a Fabry-Perrot interferometer to fade out at the receiver before reflections of a new interrogation pulse or signal sequence arrives at the receiver. Because the principles of the present invention enable interrogating time-multiplexed interferometric sensors without requiring time delays to fade out reflections of the interrogation pulses from prior interrogations, the inventive principles can enhance the signal-to-noise ratio of sensor measurements. The principles of the present invention represent an enhancement of the two pulse heterodyne sub-carrier technique in a manner such that the phase difference between any two subsequent pulses within one repetition period always changes by the same amount from one repetition period to the next.
The phase modulator 106 modulates the phase of the pulses such that the optical frequencies produced in different transmission time-slots are different. In a preferred embodiment, the difference in optical frequency between any two subsequent transmitted time-slots equals Δν, where Δν is the sub-carrier frequency. These requirements are satisfied if the phase of the pulse output by the phase modulator in the mth transmission time-slot and ith TDM repetition period is given by,
By the term “time slot” we in general mean a period of time that occurs at a certain position within every TDM period. To generate the phase shift described by Eq. (1), assuming that the phase modulator has a linear response, the voltage that has to be applied to the phase modulator 106 is proportional to:
The optical frequency of the pulses in time-slot m is given by
where ν0 is an optical frequency offset.
Thus, the pulses in two consecutive time slots are separated in frequency by Δν, so the phase function in Eq. (1) has a period equal to the sub-carrier period 1/Δν. The foregoing phase function can alternatively be generated using a frequency shifter 150, such as a Bragg cell, which linearly sweeps over a frequency range equal to the free spectral range 1/τs within one sub-carrier period 1/Δν.
l j(m,i)∝cos(φ(m,i)−φ(m−j,i)+jφ s)=cos(2πjΔνTi+jφ s). (4)
Here, m(m=j, . . . ,Np−1) is the transmission time slot number and i is the TDM period number of the original source pulse. The total detected intensity of the interference pattern is denoted l(m,i) and is the sum of all contributions lj(m,i), j=1,2, . . . ,Np−1.
The foregoing shows that the sensor phase accumulates when the light passes multiple times through the cavity [as indicated by the term jφs in Eq. (4)]. If the components of the detected intensity signal that are due to interference between reflections with a time-delay difference other than τs are not removed, the demodulated signal will be distorted. Interference between the reflections with a difference in time-delay equal to the sensor delay imbalance τs will contribute to signal components at the sub-carrier frequency Δν in the detected interference signal, while interference between reflections with time-delay differences equal to multiples of the sensor delay imbalance τs will only produce signal components at multiples of Δν. This allows for filtering away the unwanted contributions that would have given distortion of the signal. Only the band around Δν is used to extract the sensor phase. The sensor phase can be found from:
Here, l(m,i) is the detected intensity of the interference pulse in receiver time slot m and TDM period i. The inner summations in the expressions for Xc and Xs in Eq. (6) sums the Np−1 pulses received within one TDM repetition period. These sums are mixed with cosine and sine terms at the sub-carrier frequency and convolved with a low-pass filter impulse response h of length M to extract the sine and cosine components of the inner sum signals at the sub-carrier frequency Xs(k) and Xc(k), respectively. The signals Xs(k) and Xc(k) thus contain one sample each per sub-carrier period. One sample of φs from each sub-carrier period is calculated by applying Xs(k) and Xc(k) to a four quadrant phase extraction (arctan) formula. K=1/(ΔνT) is the number of repetition periods per sub-carrier period. K should be an integer and Δν and T should be chosen accordingly.
The largest possible frequency component that can be generated in the detected interference signal is (Np−1)Δν. This frequency will occur if the impulse response of sensor network contains significant components that are separated in time by (Np−1)τs. In that case reflected components of the first pulse and the last pulse of the interrogation pulse sequence will overlap at the detector. Frequency components that are larger than 1/(2T) will be aliased to frequencies between 0 and 1/(2T), e.g. a frequency component at 1/(2T)<f<1/T will be aliased to a frequency 1/T−f. If a signal component is aliased to the frequency band around Δν, the extracted sensor phase will be distorted. Consequently, the largest possible frequency component that should be allowed to be generated with amplitudes that are high enough to cause unacceptable distortion is 1/T−2Δν. This implies that the maximum number of interrogating pulses Np in a sequence is determined by,
The sensor phase is calculated from the Np−1 reflected pulses from each repetition period that involves interference between first order reflections within the sensor cavity. However, there will be an infinite number of decay pulses that is produced by the multiple reflections within the Fabry-Perot cavity. The sequence of these pulses must be allowed to fade out to a level that is below the maximum allowable crosstalk level of the sensor array before a reflected pulse sequence from another sensor can be received. The number of the sequence of decay pulses that must be received before a new sequence of reflected pulses can be received, depends on the reflectivity of the reflectors.
With Ndecay decay pulses, the total length of the received pulse sequence is Np+Ndecay. With a total of N time multiplexed sensors, the minimum repetition period required is therefore,
T=N(N p +N decay))τs (8)
It can be shown that total reflected power is optimized when both Eqs. (7)and (8) are satisfied, while the distance between the sensors are selected such that Ndecay=Np, and the reflectivity is determined by the maximum allowable crosstalk level. Thus, the optimum number of interrogation pulses is:
The corresponding reflectivites becomes,
where Xrel is the maximum allowable crosstalk level. When compared to the two pulse interrogation method, the foregoing method has a potential of increasing the signal-to-noise ratio.
Crosstalk between sensors with moderate reflectivity may be relatively high when TDM multiplexing several Fabry-Perot sensors on the same line using any of the TDM interrogation methods discussed herein. Therefore, for some embodiments, couplers 122 that split the power into parallel optical waveguides 120 having one TDM sensor per fiber may be utilized. Further, for some embodiments, the interrogation techniques described herein may be combined with wavelength division multiplexing (WDM) by using gratings at different wavelengths as reflectors.
While the foregoing description is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3149492||Mar 6, 1961||Sep 22, 1964||Astra Inc||Fluid pressure gauge|
|US3851521||Jan 19, 1973||Dec 3, 1974||M & J Valve Co||System and method for locating breaks in liquid pipelines|
|US4080837||Dec 3, 1976||Mar 28, 1978||Continental Oil Company||Sonic measurement of flow rate and water content of oil-water streams|
|US4114439||Aug 18, 1977||Sep 19, 1978||Danfoss A/S||Apparatus for ultrasonically measuring physical parameters of flowing media|
|US4144768||Jan 3, 1978||Mar 20, 1979||The Boeing Company||Apparatus for analyzing complex acoustic fields within a duct|
|US4159646||Jan 20, 1978||Jul 3, 1979||Danfoss A/S||Apparatus for measuring the flow quantity or associated parameters of a liquid with two ultrasonic transducers|
|US4164865||Jul 24, 1978||Aug 21, 1979||The Perkin-Elmer Corporation||Acoustical wave flowmeter|
|US4236406||Dec 11, 1978||Dec 2, 1980||Conoco, Inc.||Method and apparatus for sonic velocity type water cut measurement|
|US4275602||Sep 25, 1979||Jun 30, 1981||Nissan Motor Company, Limited||Fluid flow measuring apparatus|
|US4445389||Sep 10, 1981||May 1, 1984||The United States Of America As Represented By The Secretary Of Commerce||Long wavelength acoustic flowmeter|
|US4499418||Aug 5, 1982||Feb 12, 1985||Texaco Inc.||Water cut monitoring means and method|
|US4515473||Sep 13, 1984||May 7, 1985||Geo-Centers, Inc.||Photoelastic stress sensor signal processor|
|US4520320||Feb 22, 1984||May 28, 1985||The United States Of America As Represented By The Secretary Of Commerce||Synchronous phase marker and amplitude detector|
|US4546649||Sep 27, 1982||Oct 15, 1985||Kantor Frederick W||Instrumentation and control system and method for fluid transport and processing|
|US4706501||Nov 9, 1981||Nov 17, 1987||Imperial Chemical Industries Plc||Detection of step charges of pressure in vessels and apparatus therefor|
|US4788852||Nov 28, 1986||Dec 6, 1988||Petro-Canada Inc.||Metering choke|
|US4813270||Mar 4, 1988||Mar 21, 1989||Atlantic Richfield Company||System for measuring multiphase fluid flow|
|US4862750||Feb 11, 1987||Sep 5, 1989||Nice Gerald J||Vortex shedding fluid velocity meter|
|US4864868||Dec 4, 1987||Sep 12, 1989||Schlumberger Industries, Inc.||Vortex flowmeter transducer|
|US4884457||Mar 23, 1989||Dec 5, 1989||Texaco Inc.||Means and method for monitoring the flow of a multi-phase petroleum stream|
|US4896540||Apr 8, 1988||Jan 30, 1990||Parthasarathy Shakkottai||Aeroacoustic flowmeter|
|US4932262||Jun 26, 1989||Jun 12, 1990||General Motors Corporation||Miniature fiber optic pressure sensor|
|US4947127||Feb 23, 1989||Aug 7, 1990||Texaco Inc.||Microwave water cut monitor|
|US4950883||Dec 27, 1988||Aug 21, 1990||United Technologies Corporation||Fiber optic sensor arrangement having reflective gratings responsive to particular wavelengths|
|US4976151||Mar 15, 1990||Dec 11, 1990||Sharp Kabushiki Kaisha||Method and device for detecting blocked condition in a tube of a liquid infusion pump|
|US4996419||Dec 26, 1989||Feb 26, 1991||United Technologies Corporation||Distributed multiplexed optical fiber Bragg grating sensor arrangeement|
|US5024099||Nov 20, 1989||Jun 18, 1991||Setra Systems, Inc.||Pressure transducer with flow-through measurement capability|
|US5031460||Jan 31, 1990||Jul 16, 1991||Daikin Industries, Ltd.||Transducer for detecting pressure changes in pipes|
|US5040415||Jun 15, 1990||Aug 20, 1991||Rockwell International Corporation||Nonintrusive flow sensing system|
|US5051922||Jul 21, 1989||Sep 24, 1991||Haluk Toral||Method and apparatus for the measurement of gas/liquid flow|
|US5058437||Sep 22, 1989||Oct 22, 1991||Gaz De France||Determining the quantity yield of a compressible fluid flowing through a pressure reducing valve|
|US5083452||Dec 16, 1988||Jan 28, 1992||Sensorteknikk A/S||Method for recording multi-phase flows through a transport system|
|US5099697||Nov 16, 1990||Mar 31, 1992||Agar Corporation Ltd.||Two and three-phase flow measurement|
|US5115670||Mar 9, 1990||May 26, 1992||Chevron Research & Technology Company||Measurement of fluid properties of two-phase fluids using an ultrasonic meter|
|US5152181||Jan 17, 1991||Oct 6, 1992||Lew Hyok S||Mass-volume vortex flowmeter|
|US5207107||Jun 20, 1991||May 4, 1993||Exxon Research And Engineering Company||Non-intrusive flow meter for the liquid based on solid, liquid or gas borne sound|
|US5218197||May 20, 1991||Jun 8, 1993||The United States Of America As Represented By The Secretary Of The Navy||Method and apparatus for the non-invasive measurement of pressure inside pipes using a fiber optic interferometer sensor|
|US5317576||Feb 1, 1993||May 31, 1994||United Technologies Corporation||Continously tunable single-mode rare-earth doped pumped laser arrangement|
|US5321991||May 25, 1993||Jun 21, 1994||Micro Motion Incorporated||Coriolis effect mass flowmeter|
|US5347873||Sep 9, 1993||Sep 20, 1994||Badger Meter, Inc.||Double wing vortex flowmeter with strouhal number corrector|
|US5361130||Nov 4, 1992||Nov 1, 1994||The United States Of America As Represented By The Secretary Of The Navy||Fiber grating-based sensing system with interferometric wavelength-shift detection|
|US5363342||Apr 28, 1988||Nov 8, 1994||Litton Systems, Inc.||High performance extended fiber optic hydrophone|
|US5367911||Jun 11, 1991||Nov 29, 1994||Halliburton Logging Services, Inc.||Device for sensing fluid behavior|
|US5372046||Sep 30, 1992||Dec 13, 1994||Rosemount Inc.||Vortex flowmeter electronics|
|US5398542||Oct 16, 1992||Mar 21, 1995||Nkk Corporation||Method for determining direction of travel of a wave front and apparatus therefor|
|US5401956||Sep 29, 1993||Mar 28, 1995||United Technologies Corporation||Diagnostic system for fiber grating sensors|
|US5401959||Sep 8, 1993||Mar 28, 1995||General Electric Company||Optical temperature compensation of spectral modulation sensors by ratiometric interrogation having dichroic filters|
|US5426297||Sep 27, 1993||Jun 20, 1995||United Technologies Corporation||Multiplexed Bragg grating sensors|
|US5440932||Mar 24, 1994||Aug 15, 1995||Dynisco, Inc.||Pressure transducer including coaxial rings|
|US5493390||Aug 23, 1994||Feb 20, 1996||Finmeccanica S.P.A.-Ramo Aziendale Alenia||Integrated optical instrumentation for the diagnostics of parts by embedded or surface attached optical sensors|
|US5493512||Jan 21, 1992||Feb 20, 1996||Centre National De La Recherche Scientifique (Cnrs)||Method and apparatus for measuring unsteady flow velocity|
|US5513913||May 28, 1993||May 7, 1996||United Technologies Corporation||Active multipoint fiber laser sensor|
|US5564832||Jun 7, 1995||Oct 15, 1996||United Technologies Corporation||Birefringent active fiber laser sensor|
|US5576497||May 9, 1995||Nov 19, 1996||The Foxboro Company||Adaptive filtering for a vortex flowmeter|
|US5591922||May 16, 1995||Jan 7, 1997||Schlumberger Technology Corporation||Method and apparatus for measuring multiphase flows|
|US5597961||Jun 15, 1995||Jan 28, 1997||Texaco, Inc.||Two and three phase flow metering with a water cut monitor and an orifice plate|
|US5639667||Jun 21, 1995||Jun 17, 1997||Institut Francais Du Petrole||Process and device for monitoring by periodic excitation a flow of particles in a pipe|
|US5642098||Apr 18, 1996||Jun 24, 1997||Oems Corporation||Capacitive oil water emulsion sensor system|
|US5644093||Sep 12, 1996||Jul 1, 1997||Minnesota Mining And Manufacturing Company||Sensor mounting pad and method|
|US5654551||May 20, 1993||Aug 5, 1997||Commonwealth Scientific And Industrial Research Organisation||Method and apparatus for the measurement of the mass flow rates of fluid components in a multiphase slug flow|
|US5657405||Feb 29, 1996||Aug 12, 1997||Research Institute Of Advanced Material Gas-Generator||Optical fiber sensor for measuring pressure or displacement|
|US5670720||Jan 11, 1996||Sep 23, 1997||Morton International, Inc.||Wire-wrap low pressure sensor for pressurized gas inflators|
|US5680489||Jun 28, 1996||Oct 21, 1997||The United States Of America As Represented By The Secretary Of The Navy||Optical sensor system utilizing bragg grating sensors|
|US5689540||Oct 11, 1996||Nov 18, 1997||Schlumberger Technology Corporation||X-ray water fraction meter|
|US5708211||Jan 17, 1997||Jan 13, 1998||Ohio University||Flow regime determination and flow measurement in multiphase flow pipelines|
|US5730219||Sep 11, 1995||Mar 24, 1998||Baker Hughes Incorporated||Production wells having permanent downhole formation evaluation sensors|
|US5732776||Feb 9, 1995||Mar 31, 1998||Baker Hughes Incorporated||Downhole production well control system and method|
|US5741980||Jan 16, 1997||Apr 21, 1998||Foster-Miller, Inc.||Flow analysis system and method|
|US5754293||Jan 6, 1997||May 19, 1998||Sensor Dynamics Limited||Apparatus for the simultaneous acquisition of high bandwidth information in very long arrays containing large numbers of sensor elements|
|US5803167||Aug 20, 1997||Sep 8, 1998||Baker Hughes Incorporated||Computer controlled downhole tools for production well control|
|US5804713||Sep 20, 1995||Sep 8, 1998||Sensor Dynamics Ltd.||Apparatus for sensor installations in wells|
|US5808779||May 16, 1997||Sep 15, 1998||Rock Bit International||Optical fiber modulation and demodulation system|
|US5842347||Sep 29, 1997||Dec 1, 1998||Sengentrix, Inc.||Method and apparatus for monitoring the level of liquid nitrogen in a cryogenic storage tank|
|US5845033||Nov 7, 1996||Dec 1, 1998||The Babcock & Wilcox Company||Fiber optic sensing system for monitoring restrictions in hydrocarbon production systems|
|US5906238||Apr 1, 1997||May 25, 1999||Baker Hughes Incorporated||Downhole flow control devices|
|US5907104||Dec 8, 1995||May 25, 1999||Direct Measurement Corporation||Signal processing and field proving methods and circuits for a coriolis mass flow meter|
|US5908990||Apr 18, 1997||Jun 1, 1999||Aura Enviromental, Ltd.||Apparatus for measuring the velocity of a fluid flowing in a conduit|
|US5917597||Feb 4, 1998||Jun 29, 1999||Litton Systems, Inc.||Noise suppression apparatus and method for time division multiplexed fiber optic sensor arrays|
|US5925821||Jun 8, 1998||Jul 20, 1999||Societe National Industrielle||Device for measuring noise in a pipe traversed by a fluid|
|US5925879||May 9, 1997||Jul 20, 1999||Cidra Corporation||Oil and gas well packer having fiber optic Bragg Grating sensors for downhole insitu inflation monitoring|
|US5939643||Aug 8, 1997||Aug 17, 1999||Endress + Hauser Flowtec Ag||Vortex flow sensor with a cylindrical bluff body having roughned surface|
|US5956132||May 22, 1997||Sep 21, 1999||Intellectual Property Law Dept. Schlumberger-Doll Research||Method and apparatus for optically discriminating between the phases of a three-phase fluid|
|US5959547||Sep 17, 1997||Sep 28, 1999||Baker Hughes Incorporated||Well control systems employing downhole network|
|US5963880||Apr 29, 1997||Oct 5, 1999||Schlumberger Industries, Inc.||Method for predicting water meter accuracy|
|US5975204||Sep 26, 1997||Nov 2, 1999||Baker Hughes Incorporated||Method and apparatus for the remote control and monitoring of production wells|
|US5987197||Nov 7, 1997||Nov 16, 1999||Cidra Corporation||Array topologies for implementing serial fiber Bragg grating interferometer arrays|
|US5991026||Mar 7, 1997||Nov 23, 1999||Sensor Dynamics Limited||Apparatus for multiplexing fibre-optic sensing interferometers|
|US5992519||Sep 29, 1997||Nov 30, 1999||Schlumberger Technology Corporation||Real time monitoring and control of downhole reservoirs|
|US5996690||Sep 26, 1997||Dec 7, 1999||Baker Hughes Incorporated||Apparatus for controlling and monitoring a downhole oil/water separator|
|US6002985||May 6, 1997||Dec 14, 1999||Halliburton Energy Services, Inc.||Method of controlling development of an oil or gas reservoir|
|US6003383||Sep 19, 1996||Dec 21, 1999||Schlumberger Industries, S.A.||Vortex fluid meter incorporating a double obstacle|
|US6003385||May 19, 1997||Dec 21, 1999||Schlumberger Industries, S.A.||Ultrasound apparatus for measuring the flow speed of a fluid|
|US6009216||Nov 5, 1997||Dec 28, 1999||Cidra Corporation||Coiled tubing sensor system for delivery of distributed multiplexed sensors|
|US6016702||Sep 8, 1997||Jan 25, 2000||Cidra Corporation||High sensitivity fiber optic pressure sensor for use in harsh environments|
|US6158288||Jan 28, 1999||Dec 12, 2000||Dolphin Technology, Inc.||Ultrasonic system for measuring flow rate, fluid velocity, and pipe diameter based upon time periods|
|US6195162||Oct 9, 1998||Feb 27, 2001||Geosensor Corporation||Seismic sensor with interferometric sensing apparatus|
|US6212306||Oct 7, 1999||Apr 3, 2001||David J. F. Cooper||Method and device for time domain demultiplexing of serial fiber Bragg grating sensor arrays|
|US6216532||Nov 27, 1997||Apr 17, 2001||Schlumberger Technology Corporation||Gas flow rate measurement|
|US6233374||Jun 4, 1999||May 15, 2001||Cidra Corporation||Mandrel-wound fiber optic pressure sensor|
|1||"Advances In Instrumentation and Control", Proceedings of the ISA 90 International Conference and Exhibit, New Orleans, Louisiana, Oct. 14-18, 1990, vol. 45, pp. 1889-1914.|
|2||A. P. Dowling and J. E. FFOWCS Williams, "Sound And Sources", 1983, pp. 224-229.|
|3||Alan D. Kersey, Michael A. Davis, Heather, J. Patrick, Michel LeBlanc, K.P. Koo, Member, IEEE, C.G. Askins, M.A. Putnam, and E. Joseph Friebele, "Fiber Grating Sensors", Journal of Lightwave Technology, vol. 15, No. 8, Aug. 1997, pp. 1443-1463.|
|4||Leo L. Beranek and Istvan L. Ver, "Noise and Vibration Control Engineering, Principles and Applications", 1992, pp. 537-541.|
|5||U.K. Search Report, Application No. GB0511247.9, dated Aug. 26, 2005.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8989573 *||Mar 28, 2013||Mar 24, 2015||Gwangju Institute Of Science And Technology||Sensing apparatus|
|US9146151||Nov 18, 2011||Sep 29, 2015||Optasense, Inc.||Pulse labeling for high-bandwidth fiber-optic distributed acoustic sensing with reduced cross-talk|
|US9410422||Sep 13, 2013||Aug 9, 2016||Chevron U.S.A. Inc.||Alternative gauging system for production well testing and related methods|
|US20130266321 *||Mar 28, 2013||Oct 10, 2013||Gwangju Institute Of Science And Technology||Sensing apparatus|
|International Classification||G01D5/353, H04J14/08, G02F1/21, G01D5/26, H04B10/04, G02F, G01B9/02|
|Oct 5, 2004||AS||Assignment|
Owner name: WEATHERFORD/LAMB, INC., TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:WAAGAARD, OLE HENRIK;RONNEKLEIV, ERLEND;REEL/FRAME:015214/0039
Effective date: 20040929
|Jan 5, 2005||AS||Assignment|
Owner name: OPTOPLAN AS, NORWAY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WEATHERFORD/LAMB, INC.;REEL/FRAME:015517/0984
Effective date: 20041230
|Jul 11, 2012||FPAY||Fee payment|
Year of fee payment: 4
|Jul 11, 2016||FPAY||Fee payment|
Year of fee payment: 8